Liquid delivery head, liquid delivery device, and liquid delivery head driving method

ABSTRACT

The present invention is applied to a printer that discharges ink drops by driving, for example, heater elements. In the case where a plurality of variable pressure generator elements are driven to control the direction in which the drop is discharged, the present invention makes it possible to lay out drive circuits and so on efficiently so as to arrange nozzles in a high density. According to the present invention, in the case where a plurality of variable pressure generator elements  15 A and  15 B are provided for a liquid chamber, and are controlled to control the direction in which the drop is discharged, a sub-control circuit  31  varies the balance between the variable pressure generator elements  15 A and  15 B driven by a main control circuit  27 . Since the current concerning the sub-control circuit  31  is small, the wiring pattern concerning the sub-control circuit  31  is formed in a narrow width.

BACKGROUND OF INVENTION

The present invention relates to a liquid discharging head whichdischarges liquid in a liquid chamber from a nozzle using energy such asthermal energy, a liquid discharging apparatus having the liquiddischarging head, and a driving method for the liquid discharging head.

Recently, in the fields of hard copy, printing, and so on, the need forcolor output has increased. In response to this need, apparatuses havebeen proposed such as image producing apparatuses and liquid dischargingapparatuses using color image production methods such as a thermal dyesublimation method; a thermal wax transfer method; an ink-jet method; anelectro-photographic method; and a thermal silver-salt developmentmethod.

A liquid discharging apparatus using the ink-jet method discharges adrop of recording liquid (ink) from a nozzle of a printer head, which isa liquid discharging head, onto a recording medium to form a dot. Theapparatus has a simple structure and can produce a high quality image.In this ink-jet method, an energy generating element applies energy tothe ink in a liquid chamber, thereby causing an ink drop to bedischarged from the nozzle. The ink-jet methods are classified accordingto the kind of energy generating element into an electrostaticattraction type; a continuous-vibration generating type (piezo type);and a thermal type.

In the thermal type, a heater element is used as the energy generatingelement. Local heating (application of energy) of the ink in the liquidchamber by the heater element generates bubbles in the ink in the liquidchamber. The pressure generated in the bubbles causes the ink to bedischarged from the nozzle onto the recording medium. An apparatus usingthe thermal-type ink-jet method has a simple structure and can print acolor image.

A liquid discharging head used in a liquid discharging apparatus usingthe thermal-type ink-jet method is manufactured by providing asemiconductor substrate with drive circuits, which are logic ICs,driving heater elements; heater elements; ink chambers; and nozzles, inthis order, as disclosed in Japanese Unexamined Patent ApplicationPublication No. 7-68759. Since the heater elements are integrated withthe drive circuits, the heater elements can be arranged at a highdensity. Therefore, high-resolution prints can be obtained.

In most of such liquid discharging heads, a head chip having thefollowing structure is used. That is to say, each nozzle is providedwith a heater element; the heater elements are aligned in a row on thesubstrate; on one side of the row, the drive circuits are provided; andon the other side thereof, an ink flow path is provided. By using such ahead chip, the liquid discharging head can be miniaturized.

Concerning such a liquid discharging head, as disclosed in JapaneseUnexamined Patent Application Publication No. 8-48034, a method forcontrolling the discharging direction of the liquid drop is proposed. Inthe method, the discharging direction of the liquid drop is controlledby separately driving a plurality of energy-generating elements providedfor each liquid chamber.

FIG. 1 shows the liquid discharging head viewed from the side where thenozzles are provided. In FIG. 1, a nozzle 1 is provided for each inkchamber 2. For each ink chamber 2, two heater elements 3A and 3B areprovided side by side in the direction in which the ink chambers 2 arealigned. As shown in FIG. 2, one end of each of the heater elements 3Aand 3B is connected to a common wiring pattern 4. The heater elements 3Aand 3B are connected to a power supply 5 via the common wiring pattern4. The other ends of each of the heater elements 3A and 3B arerespectively connected to transistors 7A and 7B via wiring patterns 6Aand 6B, respectively. The heater elements 3A and 3B are grounded via thetransistors 7A and 7B, respectively. The transistors 7A and 7B areseparately switched on at a predetermined timing according to thetiming-control of a control circuit 9 to drive the heater elements 3Aand 3B, respectively. The currents IA and IB flowing through the heaterelements 3A and 3B, respectively, are controlled based on thedetermination of gate-voltage in the on-state by the control circuit 9.The heater elements 3A and 3B have about the same shapes and about thesame resistance values. The heater elements 3A and 3B are arranged aboutsymmetrically with respect to the center line of the nozzle 1. Theliquid chamber 2 is about symmetrical with respect to the middle linebetween the heater elements 3A and 3B.

When either heater element 3A or 3B is driven, an ink drop is dischargedat an angle.

Concerning the above-described structure, in the case where each nozzle1 is provided with two heater elements 3A and 3B, where the heaterelements 3A and 3B are aligned in a row, where the drive circuits areprovided on one side of the row, and where an ink flow path is providedon the other side thereof, however, the wiring pattern 4 or the wiringpatterns 6A and 6B connected to the heater elements 3A and 3B need to bebent. In this case, as shown in FIG. 1, a drive circuit composed of thetransistors 7A and 7B and the control circuit 9 are provided on the sideof the wiring patterns 6A and 6B connecting the heater elements 3A and3B to the transistors 7A and 7B, respectively. The common wiring pattern4 is bent and led to the side of the wiring patterns 6A and 6B throughthe gap between the adjacent heater-element pairs. In this way, thedrive circuit and the wiring patterns 4, 6A, and 6B can be laid outefficiently.

The current IA or IB flowing through the individual wiring pattern 6A or6B, respectively, flows through the common wiring pattern 4. When thetransistors 7A and 7B are both driven to drive both of the heaterelements 3A and 3B, the current IA+IB flows through the common wiringpattern 4. Therefore, in the conventional structure, the width of thiscommon wiring pattern 4 needs to be greater than or equal to the sum ofthe width of the individual wiring pattern 6A and the width of theindividual wiring pattern 6B. This causes problems in that the nozzlescannot be arranged at a high density. Incidentally, in the conventionalstructure, if the width of the common wiring pattern 4 is less than thesum of the width of the individual wiring pattern 6A and the width ofthe individual wiring pattern 6B, wire breakage occurs due toelectromigration.

SUMMARY OF THE INVENTION

Considering the above, it is an object of the present invention toprovide a liquid discharging head, a liquid discharging apparatus, and adriving method for the liquid discharging head capable of laying outdrive circuits and so on efficiently so as to arrange nozzles in a highdensity, in the case where a plurality of energy generating elements aredriven to control the direction in which the drop is discharged.

To attain this object, the present invention is a liquid discharginghead or a liquid discharging apparatus including: at least one liquidchamber holding liquid; a nozzle provided for each liquid chamber; atleast one pair of energy generating elements provided for each liquidchamber, and applying energy to the liquid held in the liquid chamber todischarge the liquid from the nozzle; a main control circuit connectinga series circuit of the at least one pair of energy generating elementsto a power supply, and driving the at least one pair of energygenerating elements according to the timing for discharging the liquid;a sub-control circuit connected to a connection midpoint between the atleast one pair of energy generating elements, and varying the balance ofenergy generation between the at least one pair of energy generatingelements; a first wiring pattern connecting the connection midpoint tothe sub-control circuit; and second wiring patterns connecting the atleast one pair of energy generating elements to the main controlcircuit, wherein the first wiring pattern has a width narrower than thewidth of the second wiring pattern.

According to the present invention, when the at least one pair of energygenerating elements are driven, the driving by the sub-control circuitneeds a small current compared with the driving by the main controlcircuit which needs a large current. Therefore, the first wiring patterncan be formed in a narrow width compared with the second wiringpatterns. In the case where a plurality of energy generating elementsare driven to control the direction in which the drop is discharged,drive circuits and so on can be laid out efficiently so as to arrangethe nozzles in a high density.

In addition, the present invention is a driving method for a liquiddischarging head including a liquid chamber holding liquid; a nozzleprovided for the liquid chamber; at least one pair of energy generatingelements provided for the liquid chamber, and applying energy to theliquid held in the liquid chamber to discharge the liquid from thenozzle; a main control circuit connecting a series circuit of the atleast one pair of energy generating elements to a power supply; asub-control circuit connected to a connection midpoint between the atleast one pair of energy generating elements; a first wiring patternconnecting the connection midpoint to the sub-control circuit; andsecond wiring patterns connecting the at least one pair of energygenerating elements to the main control circuit, the driving methodincluding the steps of: driving the series circuit of the at least onepair of energy generating elements according to the timing fordischarging the liquid by the main control circuit; and varying thebalance of energy generation between the at least one pair of energygenerating elements by the sub-control circuit. The first wiring patternhas a width narrower than the width of the second wiring pattern becausethe current necessary for the sub-control circuit is smaller than thecurrent necessary for the main control circuit.

In the case where a plurality of energy generating elements are drivento control the direction in which the drop is discharged, drive circuitsand so on can be laid out efficiently so as to arrange the nozzles in ahigh density.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a layout when a plurality of heaterelements are arranged.

FIG. 2 is a connection diagram in the case where the heater elementsaccording to the structure in FIG. 1 are driven separately.

FIG. 3 is a plan view showing part of a printer head according to anembodiment of the present invention.

FIG. 4 is an exploded perspective view showing a head chip of theprinter head in FIG. 3.

FIG. 5 is a plan view showing the structure of the printer head.

FIGS. 6(A) and 6(B) are a plan view and a sectional view, respectively,showing an ink chamber.

FIG. 7 is a schematic diagram explaining the drive control in theprinter head of FIG. 3.

FIGS. 8(A), 8(B), and 8(C) are sectional views taken along lines A-A,B-B, and C-C, respectively, in FIG. 7(A).

FIG. 9 is a connection diagram showing a main control circuit and asub-control circuit.

FIG. 10 is a plan view showing a specific layout of the head chip inFIG. 5.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The embodiments of the present invention will now be described withreference to the drawings.

(1) Structure of Embodiment

FIG. 3 is a plan view showing a printer head used in a printer accordingto this embodiment. This printer head 11 is a line head. An ink flowpath 12 connected to an ink tank is formed of a predetermined member soas to extend across the width of paper as an object of printing. Oneither side of the ink flow path 12, head chips 13 are staggered. Eachhead chip 13 has a row of ink discharging mechanisms.

The head chip 13 is formed in a rectangular-solid shape. Along itslongitudinal face, nozzles 14 are formed at a fixed nozzle pitch. Theink supplied from the ink flow path 12 is discharged from the nozzles14. In such a staggered arrangement, the head chips 13 are arranged sothat the nozzles 14 are arranged at a fixed nozzle pitch in thealignment direction of the nozzles 14, even between the head chips 13adjacent to each other. The printer head 11 can print a desired image bydriving the head chips 13 arranged across the width of the paper.

If the nozzles 14 are arranged at a high density, the nozzle pitch isnarrower. Therefore, due to an error in fitting of the head chips 13,variation in the nozzle pitch becomes large at the joint between thehead chips 13 adjacent to each other. In this embodiment, controllingthe direction in which the ink drop is discharged from the head chip 13makes it possible to compensate for the variation in the nozzle pitchbetween the head chips 13 adjacent to each other.

As shown in FIG. 4, the head chip 13 is manufactured by providing asemiconductor substrate 16 with a separating wall 18 so as to form inkchambers 17, and thereafter providing a nozzle plate 20. On thesemiconductor substrate 16, drive circuits driving heater elements 15Aand 15B are provided. In the nozzle plate 20, the nozzles 14 are formed.In the head chip 13, as shown in FIG. 5, the heater elements 15A and 15Bare aligned along the longitudinal face facing the ink flow path 12. Inthe region along this face, a heater element section is thus formed. Inaddition, from this heater element section to the opposite face, a drivecircuit section and a connecting terminal section are provided in thisorder. In the drive circuit section, drive circuits driving the heaterelements 15A and 15B are arranged. In the connecting terminal section,connecting terminals connecting the driver circuits to a power supplyand so on are arranged.

The ink in the ink flow path 12 is led to the ink chambers 17 from theface adjacent to the heater elements 15A and 15B. The drive circuits areprovided across the row of the heater elements 15A and 15B from the inkflow path 12. Thus, in the head chip 13, the heater elements 15A and15B, the drive circuits, and so on are laid out efficiently. The headchips 13 are manufactured efficiently by providing or forming the drivecircuits, the heater elements, and the ink chambers for a plurality ofchips on a semiconductor wafer, thereafter cutting the semiconductorwafer into a plurality of chips, and then attaching a nozzle plate 20 toeach chip.

As shown in FIG. 6(A), a plan view, and FIG. 6(B), a sectional view,each liquid chamber 17 is provided with a pair of heater elements 15Aand 15B. The pair of heater elements 15A and 15B have about the sameshapes and about the same resistance values, and are arranged side byside in the direction in which the liquid chambers 17 are aligned. FIG.6(A) is a plan view with the nozzle plate 20 removed. The printer head11 can control the direction in which the ink drop is discharged bycontrolling the driving of the heater elements 15A and 15B, which areenergy generating elements applying energy to the ink in the ink chamber17.

FIG. 7 is a connection diagram explaining the principle of controllingthe driving of the heater elements 15A and 15B. In the head chip 13, onthe side of the ink flow path 12, the heater elements 15A and 15B areconnected by a wiring pattern 22, and thereby a series circuit of theheater elements 15A and 15B is formed. In addition, on the opposite sideof the heater elements 15A and 15B from the ink flow path 12, the heaterelements 15A and 15B are connected to wiring patterns 22A and 22B,respectively. The wiring patterns 22A and 22B are connected to the maincontrol circuit 27. The main control circuit 27 is a drive circuitdriving the series circuit of the heater elements 15A and 15B in thetiming for discharging the ink drop. The main control circuit 27connects the series circuit of the heater elements 15A and 15B to thepower supply 25 via a switching circuit 24.

Moreover, in the head chip 13, the connection midpoint between theheater elements 15A and 15B connected by the wiring pattern 22 isconnected to the sub-control circuit 31. According to the direction inwhich the ink drop is discharged, the sub-control circuit 31 varies thecurrents applied by the main control circuit 27 to the heater elements15A and 15B. That is to say, according to the direction in which the inkdrop is discharged, the sub-control circuit 31 switches contacts of aselector 28 which is connected to the wiring pattern 22, thereby varyingthe balance between the energies generated by the heater elements 15Aand 15B. Such a balance control can be performed by switching betweeninflow and outflow of the current into and out of the connectionmidpoint between the heater elements 15A and 15B, and by varying thevalue of inflow or outflow of current. This can also be performed byvarying the electric potential of the connection midpoint. In FIG. 7,such a mechanism to vary the electric potential or the current iscomposed of the selector 28, a power supply 29, and resistors 30A to30D. That is to say, when the resistor 30A or 30B connected to the powersupply 29 is selected, the selector 28 allows the current to flow intothe connection midpoint between the heater elements 15A and 15B. Thecurrent is determined by the resistance values of the heater elements15A and 15B, the resistance value of the resistor 30A or 30B, and thevoltage of the power supply 29. When the contact to which nothing isconnected is selected, the selector 28 stops varying the balance betweenthe energies generated by the heater elements 15A and 15B. When thegrounded resistor 30C or 30D is selected, the selector 28 allows thecurrent to flow out of the connection midpoint between the heaterelements 15A and 15B. The current is determined by the resistance valuesof the heater elements 15A and 15B and the resistance value of theresistor 30C or 30D.

Compared with the driving by the main control circuit 27, which needs alarge current, the driving by the sub-control circuit 31 only needs asmall current. Therefore, a wiring pattern 22C connecting the heaterelements 15A and 15B to the sub-control circuit 31 can be narrowcompared with the wiring pattern 22A or 22B provided for the heaterelements 15A or 15B, respectively.

In the case of the structure described above with reference to FIG. 1,when the resistance values of the heater elements 3A and 3B are 50 [Ω]each, and when the heater elements 3A and 3B are driven by an electricpower of 0.5 [W] each, a current of 0.2 [A] flows through the commonwiring pattern 4. In this case, when the common wiring pattern 4 has athickness of 600 [nm], and when the wiring pattern 4 has a width of 15[μm] for a current of 0.1 [A] for sake of safety, the wiring pattern 4needs a width of 30 [μm]. In addition, the wiring patterns 6A and 6Beach need a width of 15 [μm]. Therefore, the nozzle pitch is 60 [μm]even when no gap is provided between the wiring patterns. In fact, sincea gap is provided, the nozzle pitch is much wider. The nozzle pitchcannot be less than or equal to 65 [μm].

On the other hand, according to the structure shown in FIG. 7, when theheater elements 15A and 15B are each driven by an electric power of 0.5[W], no current flows through the wiring pattern 22C connected to thesub-control circuit 31. In addition, when the heating values of theheater elements 15A and 15B are different, the direction in which theink drop is discharged can be sufficiently angled by causing the drivecurrents of the heater elements 15A and 15B to differ by about tenpercent. Therefore, the width of the wiring pattern 22C needs to be onlya tenth part of that of the wiring pattern 22A or 22B. For example, whenthe heater elements 15A and 15B are driven by electric powers of 0.5 [W]and 0.4 [W], respectively, the current flowing through the wiringpatterns 22A and 22B and the current flowing through the wiring pattern22C are 0.1 [A] and 0.089 [A], respectively.

FIGS. 8(A), 8(B), and 8(C) are sectional views taken along lines A-A,B-B, and C-C, respectively, of FIG. 7. In the head chip 13, the width ofthe wiring pattern 22C is about a tenth part of that of the wiringpattern 22A or 22B. In addition, the wiring pattern 22C is disposed inthe same layer as the wiring patterns 22A and 22B, and in the gapbetween the shown heater element 15B and the heater element 15A (notshown) provided for the adjacent ink chamber 17. Thus, sufficient spaceis obtained in the head chip 13, so that the nozzle pitch of the headchip 13 is 42.3 [nm]. In FIG. 7, the reference numerals 41, 42, and 43denote interlayer insulating films of silicon nitride, and the referencenumeral 44 denotes a cavitation-resistant layer of a tantalum film.

In this embodiment, the head chip 13 is made by forming a tantalum filmwith a thickness of 80 [nm] by sputtering, and thereafter forming theheater elements 15A and 15B with predetermined shapes by lithography andetching. The heater elements 15A and 15B have a resistance value of 105[Ω] each. In this embodiment, the heater elements 15A and 15B are drivenby an electric power of 0.8 [W] to discharge the ink drop. Thesub-control circuit 31 causes a current of up to ±0.01 [A] to flowthrough the wiring pattern 22C, thereby causing the heater elements 15Aand 15B to differ in their operation.

Under this condition, in the case where the heater elements 15A and 15Bare not caused to differ in their operation, a current of 0.087 [A]flows through each of the heater elements 15A and 15B. Therefore, thewidth of each of the wiring patterns 22A and 22B is set to 15 [μm]. Thewidth of the wiring pattern 22C is set to 1.7 [μm] (15 [μm]×0.087[A]/0.01 [A]).

FIG. 9 is a connection diagram showing specific structures of the maincontrol circuit 27 and the sub-control circuit 31. The main controlcircuit 27 will be described. One end of the series circuit of theheater elements 15A and 15B is connected to the power supply 50, and theother end is grounded via a constant current circuit 51 which is aMOSFET. The operation of the constant current circuit 51 is controlledby a predetermined control signal SC1 via an AND circuit 52 which is aninverter circuit. The signal level of the control signal SC1 is raisedby an image-data processing circuit (not shown) in timings when inkdrops are discharged according to paper feed from the nozzle 14 to whichthe main control circuit 27 is allotted. In these timings, the seriescircuit of the heater elements 15A and 15B is driven by the power supply50.

The sub-control circuit 31 is composed of power supply circuits 55A,55B, 55C, and 55D which cause a predetermined value of current to flowinto or out of the connection midpoint between the heater elements 15Aand 15B. The proportion of values of the current caused to flow into orout of the connection midpoint by the power supply circuits 55A, 55B,55C, and 55D is set to 4:2:1:1 based on a setting of a constant currentcircuit included in each power supply circuit. According to controlsignals SA, SB, SC, and SD, the power supply circuits 55A, 55B, 55C, and55D, respectively, cause the heater elements 15A and 15B to differ intheir operation based on the above values of current. Other than theabove, the power supply circuits 55A, 55B, 55C, and 55D have the samestructure. Therefore, the power supply circuits 55A alone will bedescribed in detail.

In this embodiment, the proportion of current values of the power supplycircuits 55A, 55B, 55C, and 55D is set to 4:2:2:1. Between the powersupply circuits 55A, 55B, and 55C, the current value varies gradually inthe manner of a factorial of two. Therefore, this embodiment as a wholehas a simple structure, and the heater elements 15A and 15B are causedto differ in their operation efficiently.

In this embodiment, the control signals SA, SB, SC, and SD aredetermined so that the ink drops discharged from the nozzles 14 are in apredetermined pitch. This compensates for the variation in the positionof the ink dot due to manufacturing variations such as an error infitting of the head chips 13. Therefore, the quality of printing resultsis much higher than that of the conventional printer head.

A direction switching signal SC3 switches between the current inflow andthe current outflow into and out of the connection midpoint between theheater elements 15A and 15B. In the power supply circuit 55A, thedirection switching signal SC3 is input into an exclusive NOR circuit57. According to the direction switching signal SC3, the exclusive NORcircuit 57 switches the polarity of the control signal SA. In the powersupply circuit 55A, a signal output from this exclusive NOR circuit 57is input directly into an AND circuit 59. The signal is also input intoanother AND circuit 61 via an inverter circuit 60, which reverses thepolarity of the signal. The AND circuits 59 and 61 gate the outputsignal of the exclusive NOR circuit 57 and the output signal of theinverter circuit 60, respectively, according to the control signal SC1,and output them to the MOSFETs 62 and 63, respectively. While the heaterelements 15A and 15B are driven according to the control signal SC1, theMOSFETs 62 and 63 are on/off-controlled complementarily according to thedirection switching signal SC3 and the control signal SA.

In the power supply circuit 55A, the constant current circuit 58, whichis a MOSFET, is on/off-controlled according to the control signal SC2 tocause the heater elements 15A and 15B to differ in their operation ornot to cause. In the power supply circuits 55A to 55C, the proportion ofvalues of current for causing the heater elements 15A and 15B to differin their operation is set to 4:2:1:1 based on a setting of this constantcurrent circuit 58.

The sources of the MOSFETs 62 and 63 are connected to this constantcurrent circuit 58. The drain of the MOSFET 62 is connected to theconnection midpoint between the heater elements 15A and 15B. The drainof the MOSFET 63 is connected to a current mirror circuit consisting ofMOSFETs 64 and 65 provided on the power supply side. The MOSFET 65 ofthis current mirror circuit causes a constant current to flow into theconnection midpoint between the heater elements 15A and 15B. Thisconstant current has the same current value as that of the constantcurrent circuit 58. While the heater elements 15A and 15B are drivenaccording to the control signal SC1, the MOSFETs 62 and 63 areon/off-controlled complementarily according to the direction switchingsignal SC3 and the control signal SA. The constant current circuit 58,which is the standard of operation, operates according to the controlsignal SC2. In order to cause the heater elements 15A and 15B to differin their operation, when the current flows out of the connectionmidpoint, the MOSFET 62 is switched on to allow the constant currentcircuit 58 to absorb the current. On the other hand, when the currentflows into the connection midpoint, the MOSFET 63 is switched on toallow the constant current circuit 58 to discharge the current. In thisway, the direction in which the ink drop is discharged from the nozzle14 is controlled by the heater elements 15A and 15B.

FIG. 10 is a plan view showing a specific layout of the head chip havingsuch a main control circuit 27 and a sub-control circuit 31. In the headchip 13, drive circuit units are arranged side by side in thelongitudinal direction corresponding to the arrangement of the nozzles14 (FIG. 10(A)). Each unit drives the heater elements 15A and 15B foreach liquid chamber 17. In each unit, the wiring pattern 22, the wiringpattern 22C, the heater elements 15A and 15B, and the wiring pattern 22Aand 22B are arranged in this order from the side of the ink flow path.The wiring pattern 22 connects the heater elements 15A and 15B inseries. The wiring pattern 22C connects this wiring pattern 22 to thesub-control circuit 31. The wiring patterns 22A and 22B connect theheater elements 15A and 15B, respectively, to the main control circuit27. In the adjacent region AR1, the MOSFET 51 of the main controlcircuit 27, and the MOSFETs 62 to 65 of the sub-control circuit 31 aredisposed. In the next region AR2, the other components of thesub-control circuit 31 are disposed. In the further next region AR3, theother components of the main control circuit, and a control circuitcontrolling operation of the main control circuit and the sub-controlcircuit are disposed. In this way, the drive circuits for the heaterelements 15A and 15B are disposed in the regions AR1 to AR3.

(2) Operation of Embodiment

In this printer having the above structure, based on image data, textdata, and so on to print, ink drops are discharged from the printer head11. The paper as an object of printing is conveyed by a paper feedmechanism. The ink drops adhere to the paper being conveyed. In thisway, an image, a text, and so on are printed according to the operationof the printer head 11 (FIG. 7).

In the printer head 11 of the conventional printer, a plurality of headchips 13 are staggered. Each head chip 13 has ink dischargingmechanisms. There is variation in the nozzle pitch due to variation inthe arrangement of the head chips 13. In addition, there is variation inthe characteristics of the head chip 13. Therefore, the position of theink drop discharged from the nozzle 14 and adhering to the paper varieson a minute scale. This causes deterioration in the quality of print,and in an extreme case, vertical lines.

However, in the printer according to the present invention, the positionwhere the ink drop adheres to the paper is corrected by tuning thedirection in which the ink drop is discharged from the nozzle 14. Inthis way, deterioration in the quality of print is preventedefficiently. The ink drop is discharged by a so-called thermal typemethod by driving a plurality of heater elements 15A and 15B providedfor each ink chamber 17. The plurality of heater elements are caused todiffer in their operation. In this way, the direction in which the inkdrop is discharged from the nozzle 14 is tuned (FIGS. 4 and 7).

In the printer of the present invention, the main control circuit 27connects the series circuit of the heater elements 15A and 15B to thepower supply 25 in a predetermined timing to drive and operate theheater elements 15A and 15B. At this time, the sub-control circuit 31causes an inflow or an outflow of current into or out of the connectionmidpoint between the heater elements 15A and 15B to cause the heaterelements 15A and 15B to differ in their operation. The current value ofthe inflow or the outflow is set to a tenth part at a maximum of thecurrent concerning the main control circuit 27.

The width of the wiring pattern 22C can be set to about a tenth part ofthe width of the wiring pattern 22A or 22B. The wiring pattern 22Cconnects the sub-control circuit 31 and the connection midpoint betweenthe heater elements 15A and 15B. The wiring patterns 22A and 22B connectthe main control circuit 27 to the series circuit of the heater elements15A and 15B. In the printer of the present invention, even when thewiring pattern 22C is bent toward the wiring patterns 22A and 22B andwhen the wiring pattern 22C is disposed in the same layer as the wiringpatterns 22A and 22B, the nozzle pitch can be very small compared withthe structure described above with reference to FIG. 1, and therefore adesired image can be printed at a high resolution.

In addition, the heater elements and the drive circuits can be laid outefficiently by arranging the nozzles at a small pitch, arranging theheater elements 15A and 15B side by side in the direction of the row ofthe nozzles 14, supplying ink from one side of the row of the nozzles,and disposing the main control circuits and the sub-control circuits onthe other side of the row of the nozzles.

(3) Other Embodiments

Although the heater elements are made of a thin film of tantalum in theabove embodiment, the present invention is not limited to this. Theheater elements may be made of various resistor materials such astungsten, nichrome, nickel, polysilicon, and titanium nitride.

Although the heater elements are driven or caused to differ in theiroperation by current drive in the above embodiment, the presentinvention is not limited to this. The heater elements may be driven orcaused to differ in their operation by voltage drive.

Although two heater elements are provided for an ink chamber in theabove embodiment, the present invention is not limited to this. Three ormore heater elements may be provided. In this case, the plurality ofheater elements are arranged side by side and connected in series. Eachconnection midpoint between the heater elements is connected to thesub-control circuit. The heater elements are caused to differ in theiroperation in the direction in which the heater elements are arrangedside by side.

Although the heater elements are arranged side by side in the aboveembodiment, the present invention is not limited to this. The heaterelements may be arranged in a radial pattern so that the ink drop isdischarged in various directions. In this case, the number of heaterelements is set to an even number. Each pair of heater elements disposedopposite each other is connected in series. Each connection midpointbetween the pair of heater elements is connected to the sub-controlcircuit. Alternatively, all of the heater elements are connected in thecenter. The plurality of heater elements are driven by a phase feedmethod typified by a so-called Y-connection. The connection center isconnected to the sub-control circuit. Alternatively, these may becombined.

Although the heater elements and the drive circuits are integrated onthe semiconductor substrate in the above embodiment, the presentinvention is not limited to this. The heater elements and the drivecircuits may be separated.

Although controlling the direction in which the ink drop is dischargedis used for compensating for the variation in the position where the inkdrop adheres on the paper in the above embodiment, the present inventionis not limited to this. The controlling of the direction in which theink drop is discharged may be used for increasing the quality of print,and for simplifying the structure, for example, in the case where aplurality of dots are formed by a single nozzle in order to increaseresolution.

Although the present invention is applied to a thermal type line printerwhose energy generating elements are heater elements in the aboveembodiment, the present invention is not limited to this. The presentinvention may be applied to printers or printer heads having other typesof energy generating elements such as a piezo type and an electrostatictype.

Although the present invention is applied to a printer head dischargingink drops in the above embodiment, the present invention is not limitedto this. The present invention may be applied to printer heads thatdischarge drops of various dyes, or drops of liquid for forming aprotective layer, instead of ink drops. In addition, the presentinvention may be applied to micro dispensers, measuring apparatuses, andtesting apparatuses that discharge drops of a reagent. Moreover, thepresent invention may be applied to pattern producing apparatuses thatdischarge drops of an agent protecting a member from etching.

INDUSTRIAL APPLICABILITY

As described above, when the direction in which the liquid drop isdischarged is controlled by controlling operation of a plurality ofheater elements which are energy generating elements provided for eachliquid chamber, a main control circuit drives the heater elements, and asub-control circuit varies the balance between the heater elements.Since the current concerning the sub-control circuit is small, thewiring pattern concerning the sub-control circuit can be formed in anarrow width. Therefore, when the direction in which the liquid drop isdischarged is controlled by controlling operation of the plurality ofenergy generating elements, drive circuits and so on can be laid outefficiently to arrange nozzles in a high density.

That is to say, drive circuits and so on can be laid out efficiently toarrange nozzles in a high density by forming the wiring patternconcerning the sub-control circuit in a narrow width; arranging theheater elements side by side in a row in the direction in which thenozzles are aligned; providing the main control circuit and thesub-control circuit on one side of the row; providing an ink flow pathon the other side thereof; and leading the wiring pattern concerning thesub-control circuit from the side of the flow path to the sub-controlcircuit via the gap between adjacent groups of the heater elements.

1. A liquid discharging head comprising: at least one liquid chamberholding liquid; a nozzle provided for each liquid chamber; at least onepair of energy generating elements provided for each liquid chamber, andapplying energy to the liquid held in the liquid chamber to dischargethe liquid from the nozzle; a main control circuit connecting a seriescircuit of the at least one pair of energy generating elements to apower supply, and driving the at least one pair of energy generatingelements according to the timing for discharging the liquid; asub-control circuit connected to a connection midpoint between the atleast one pair of energy generating elements, and varying the balance ofenergy generation between the at least one pair of energy generatingelements; a first wiring pattern connecting the connection midpoint tothe sub-control circuit; and second wiring patterns connecting the atleast one pair of energy generating elements to the main controlcircuit, wherein, the first wiring pattern has a width narrower than thewidth of the second wiring pattern, and the sub-control circuitcomprises a selector including a switch connected to the connectionmidpoint between the at least one pair of energy generating elements andselectively connectable to: (a) a first contact connected to a resistorand a power supply; (b) a second contact that is not connected to thepower supply or to ground; and (c) a third contact connected to aresistor and ground, so that current flows from the sub-control circuitto the connection midpoint between the at least one pair of energygenerating elements when the selector switch is connected to the firstcontact of said three contacts, current does not flow between thesub-control circuit and the connection midpoint between the at least onepair of energy generating elements when the selector switch is connectedto the second contact of the three contacts, and current flows to thesub-control circuit from the connection midpoint between the at leastone pair of energy generating elements when the selector switch isconnected to the third contact of said three contacts is selected duringoperation of the liquid discharging head.
 2. The liquid discharging headaccording to claim 1, wherein the energy generating element is a heaterelement.
 3. The liquid discharging head according to claim 1, whereinthe at least one liquid chamber are arranged in a row; the at least onepair of energy generating elements are arranged in a row along the rowof the liquid chambers; the at least one pair of energy generatingelements, the main control circuit, and the sub-control circuit areprovided on a semiconductor substrate; the main control circuit and thesub-control circuit are disposed on one side of the row of the energygenerating elements, and a flow path supplying the liquid chambers withthe liquid is disposed on the other side thereof; the first wiringpattern is led from the side of the flow path to the sub-control circuitvia the gap between adjacent groups of the energy generating elements.4. The liquid discharging head according to claim 1, wherein thesub-control circuit is configured to vary the balance of energygeneration between the at least one pair of energy generating elementsby selectively sending current to and drawing current from theconnection midpoint between the at least one pair of energy generatingelements thereby controlling an electric potential between the at leastone pair of energy generating elements.
 5. The liquid discharging headaccording to claim 1, wherein the selector includes a fourth contact anda fifth contact connectable to the connection midpoint between the atleast one pair of energy generating elements by way of said switch, thefourth contact being connected to a resistor and the power supply andthe fifth contact being connected to a resistor and ground, so thatcurrent flows from the sub-control circuit to the connection midpointbetween the at least one pair of energy generating elements when theselector switch is connected to the fourth contact, current flows to thesub-control circuit from the connection midpoint between the at leastone pair of energy generating elements when the selector switch isconnected to the fifth contact during operation of the liquiddischarging head, and wherein the resistor connected to the firstcontact has a resistance that is different than a resistance of theresistor connected to the first contact and the resistor connected tothe third contact has a resistance that is different than a resistanceof the resistor connected to the fifth contact.
 6. The liquiddischarging head according to claim 1, wherein each pair of energygenerating elements of said at least one pair of energy generatingelements is separated by a gap.
 7. The liquid discharging head accordingto claim 1 further comprising at least two pairs of energy generatingelements.
 8. The liquid discharging head according to claim 7, whereinsaid at least two pairs of energy generating elements are arranged in arow.
 9. The liquid discharging head according to claim 7, wherein saidat least two pairs of energy generating elements are positioned in aradial pattern.
 10. The liquid discharging head according to claim 9,wherein said sub-control circuit is connected to a connection midpointbetween each pair of energy generating elements of the at least twopairs of energy generating elements.
 11. The liquid discharging headaccording to claim 9, wherein all of the energy generating elementscorresponding to a single liquid chamber are electrically connected in acenter between the energy generating elements.
 12. A liquid dischargingapparatus having a liquid discharging head, the liquid discharging headcomprising: at least one liquid chamber holding liquid; a nozzleprovided for each liquid chamber; at least one pair of energy generatingelements provided for each liquid chamber, and applying energy to theliquid held in the liquid chamber to discharge the liquid from thenozzle; a main control circuit connecting a series circuit of the atleast one pair of energy generating elements to a power supply, anddriving the at least one pair of energy generating elements according tothe timing for discharging the liquid; a sub-control circuit connectedto a connection midpoint between the at least one pair of energygenerating elements, and varying the balance of energy generationbetween the at least one pair of energy generating elements; a firstwiring pattern connecting the connection midpoint to the sub-controlcircuit; and second wiring patterns connecting the at least one pair ofenergy generating elements to the main control circuit, wherein, thefirst wiring pattern has a width narrower than the width of the secondwiring pattern, and the sub-control circuit comprises a selectorincluding a switch connected to the connection midpoint between the atleast one pair of energy generating elements and selectively connectableto: (a) a first contact connected to a resistor and a power supply; (b)a second contact that is not connected to the power supply or to groundand (c) a third contact connected to a resistor and ground, so thatcurrent flows from the sub-control circuit to the connection midpointbetween the at least one pair of energy generating elements when theselector switch is connected to the first contact of said threecontacts, current does not flow between the sub-control circuit and theconnection midpoint between the at least one pair of energy generatingelements when the selector switch is connected to the second contact ofthe three contacts, and current flows to the sub-control circuit fromthe connection midpoint between the at least one pair of energygenerating elements when the selector switch is connected to the thirdcontact of said three contacts is selected during operation of theliquid discharging head.
 13. A driving method for a liquid discharginghead comprising a liquid chamber holding liquid; a nozzle provided forthe liquid chamber; at least one pair of energy generating elementsprovided for the liquid chamber, and applying energy to the liquid heldin the liquid chamber to discharge the liquid from the nozzle; a maincontrol circuit connecting a series circuit of the at least one pair ofenergy generating elements to a power supply; a sub-control circuitconnected to a connection midpoint between the at least one pair ofenergy generating elements; a first wiring pattern connecting theconnection midpoint to the sub-control circuit; and second wiringpatterns connecting the at least one pair of energy generating elementsto the main control circuit, the driving method comprising the steps of:driving the series circuit of the at least one pair of energy generatingelements according to the timing for discharging the liquid by the maincontrol circuit; and varying the balance of energy generation betweenthe at least one pair of energy generating elements by the sub-controlcircuit, wherein, the first wiring pattern has a width narrower than thewidth of the second wiring pattern because the current necessary for thesub-control circuit is smaller than the current necessary for the maincontrol circuit, and the sub-control circuit comprises a selectorincluding a switch connected to the connection midpoint between the atleast one pair of energy generating elements and selectively connectableto: (a) a first contact connected to a resistor and a power supply; (b)a second contact that is not connected to the power supply or to groundand (c) a third contact connected to a resistor and ground, so thatcurrent flows from the sub-control circuit to the connection midpointbetween the at least one pair of energy generating elements when theselector switch is connected to the first contact of said threecontacts, current does not flow between the sub-control circuit and theconnection midpoint between the at least one pair of energy generatingelements when the selector switch is connected to the second contact ofthe three contacts, and current flows to the sub-control circuit fromthe connection midpoint between the at least one pair of energygenerating elements when the selector switch is connected to the thirdcontact of said three contacts is selected during operation of theliquid discharging head.
 14. A drive method according to claim 13wherein said step of varying the balance of energy generation betweenthe at least one pair of energy generating elements includes controllingan electrical potential between the at least one pair of energygenerating elements by selectively sending current to the midpointbetween the at least one pair of energy generating elements from thesub-control circuit, drawing current from the midpoint between the atleast one pair of energy generating elements, and not sending current toor drawing current from the midpoint between the at least one pair ofenergy generating elements.
 15. A drive method according to claim 13wherein the liquid discharging head comprises at least two pair ofenergy generating elements corresponding to the liquid chamber and saidvarying step includes varying a balance of energy generated by the atleast two pairs of energy generating elements to selectively dischargeliquid from the head in one of at least four directions.